Users: Prevent infinite loop when using capability checks during `determine_current_user` on multisite.

On multisite, when checking if a user has a certain capability WordPress makes an additional check to see if the user is a super admin. The `is_super_admin()` function contained a call to `wp_get_current_user()` so as the global current user object could be used if it matched the queried user id.

This would cause an infinite loop if a hook attached to the `determine_current_user` filter was itself making a permission check. For example when limiting who can use the Application Passwords feature based on their capabilities.

Since [50790] the `WP_User` instance for the current user is shared between `wp_get_current_user()` and `get_userdata()`. This means we can remove the `wp_get_current_user` call from `is_super_admin()` while still retaining the same behavior.

Props chrisvanpatten, peterwilsoncc.
Fixes #53386.

Built from https://develop.svn.wordpress.org/trunk@52157


git-svn-id: http://core.svn.wordpress.org/trunk@51749 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/capabilities.php

@@ -888,7 +888,7 @@ function get_super_admins() {
  * @return bool Whether the user is a site admin.
  */
 function is_super_admin( $user_id = false ) {
-	if ( ! $user_id || get_current_user_id() == $user_id ) {
+	if ( ! $user_id ) {
 		$user = wp_get_current_user();
 	} else {
 		$user = get_userdata( $user_id );

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-52156';
+$wp_version = '5.9-alpha-52157';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.